In the production of semiconductor wafers or semiconductor substrates, as pressure-sensitive adhesive sheets used for being adhered on semiconductor wafers or substrates, performing processing such as dicing and expanding, and then, picking up and simultaneously mounting the semiconductor wafers or semiconductor substrates, there have hitherto been proposed pressure-sensitive adhesive sheets including a base material having provided thereon a pressure-sensitive adhesive layer having the property of polymerizing by irradiation of ultraviolet rays or the like. In such pressure-sensitive adhesive sheets, the pressure-sensitive adhesive layers are allowed to undergo a polymerization curing reaction by irradiation of ultraviolet rays or the like after the purpose of adhesion has been achieved, thereby reducing adhesive force of the pressure-sensitive adhesive layers to be able to pick up the semiconductor wafers or semiconductor substrates. Specifically, for example, JP-A-6-49420 proposes a pressure-sensitive adhesive sheet for processing a semiconductor wafer, which includes a base material having transparency to ultraviolet rays and/or radiations and a pressure-sensitive adhesive layer that undergoes a polymerization curing reaction by ultraviolet rays and/or radiations, in which the pressure-sensitive adhesive layer includes a base polymer, a multifunctional urethane acrylate-based oligomer having a molecular weight of 15000 to 50000, a polyester-based plasticizer and a photopolymerization initiator, and the content of the polyester plasticizer is 1 to 50 parts by weight with respect to 100 parts by weight of the base polymer. Further, JP-A-62-153376 proposes a pressure-sensitive adhesive sheet including a base material having applied thereon a pressure-sensitive adhesive layer containing an adhesive and a radiation polymerizable compound, in which a multifunctional urethane acrylate oligomer having a molecular weight of about 3000 to 10000 is used as the radiation polymerizable compound.
Recently, however, there have increased wafers having marks with a depth of about 5 to 10 μm that are printed on surfaces thereof by laser irradiation. Further, also in semiconductor substrates, there have increased those having rough surfaces of about 0.4 to 15 μm on sealing resin surfaces acting as surfaces to which pressure-sensitive adhesive tapes are to be adhered, or substrates having marks with a depth of 25 to 40 μm that are printed in the same manner as with the wafers. In processing of such semiconductor wafers or semiconductor substrates having an extremely minute unevenness on their surfaces, the conventional pressure-sensitive adhesive sheets are not sufficient to follow up the unevenness on the surfaces to which the sheets are to be adhered, so that sufficient adhesive force cannot be obtained. As a result, when the wafers or substrates are cut, chips fly off to cause the occurrence of the defect of substantially decreasing the yield. Further, the chips that have flied off collide with a cutting blade to cause the occurrence of the defect of damaging the blade. Furthermore, the sheets are insufficient to follow up the unevenness, so that air bubbles are involved in depressed portions to cause the occurrence of poor curing of pressure-sensitive adhesive layers, and when the wafers or substrates are picked up after irradiation of radiations, there occurs the defect that residues of adhesives are partially observed.
Patent Document 1: JP-A-6-49420
Patent Document 2: JP-A-62-153376